Partial support is requested for the fourth and fifth FASEB Summer Conferences, Mobile Elements in Mammalian Genomes which will be held in Snowmass, CO, July 5-10, 2009. The objective of the meeting is to bring together a diverse group of investigators with a common interest in mobile DNA to discuss recent advances in how mobile elements have impacted and continue to influence the functional expression and evolution of mammalian genomes. The program comprises all aspects of mobile DNA including bioinformatic, biochemical, evolutionary, and population genetic studies on mammalian transposable elements, as well as work to exploit transposable elements for saturation mutagenesis and gene delivery. Comparative genomics provides strong evidence for mobile DNA amplification, repression and extinction in evolutionary time. The 1000 genomes project as well as a wealth of new studies on mobile element association with epigenetics and gene networks represent a particular highlight of this year's meeting. This timely conference will facilitate the sharing of exciting new findings, experimental challenges, and outstanding questions in this rapidly evolving field among students, post- doctoral trainees, and junior and senior principal investigators. This is particularly valuable in a field, such as mobile elements, that does not conform to Mendelian genetic principles, and therefore has unique needs in terms of analysis and approaches.